Analyses of the Adhesion Interphase of <i>Isotactic</i> Polypropylene Using Hot-Melt Polyolefin Adhesives
Takuya Matsumoto, Yosuke Shimizu, Takashi Nishino
Abstract
The interphase structure and properties of isotactic polypropylene (it.PP) have received much attention in the fundamental science and industrial applications for the improvement of the poor adhesion properties of the it.PP. In this work, we focused on the laminates with it.PP substrates and various ethylene–octene rubber (EOR) hot-melt adhesives with different molecular weights and crystallinities. We prepared laminate samples using EOR with low molecular weight, random copolymerized EOR, and block-like copolymerized EOR as adhesives. We performed T-peel tests of the laminate samples and evaluated their thickness of the interphase with confocal Raman scattering imaging, X-ray refraction contrast imaging, and atomic force microscopic imaging. The laminates with larger interphase thicknesses possessed the larger T-peel strengths, which were relatively consistent with these obtained results among all the measurement methods. It is revealed that the adhesion properties and the interphase thicknesses depended on the crystallinities of the it.PP substrates. These results mean that the interphase would be constructed by not only diffusion of molecular chains but also the crystalline growth and the formation of lamellae interlock in the interphase region.